The present invention relates to the preparation of optical fibers to be joined in end-to-end, butt-coupled splices or used in other mechanical connections. In particular, the invention provides a method and apparatus for quickly and effectively obtaining oblique angle endface fractures of standard commercial optical fibers. Such endfaces are desirable for the assembly of low reflection, low insertion loss mechanical splices and connections, and the use of a fracturing method to form them avoids the tedious practice of shaping the fiber ends by means of grinding and polishing, a practice which unfortunately has additional undesirable effects upon the fiber.
The efficiency of optical fiber splices relies in great measure upon the proper preparation of the fiber ends prior to the joining of the fibers. Fusion coupling and physical contact between butt-coupled fibers have been moderately successful means for acquiring effective light transmission between fibers. These practices usually require highly precise, perpendicular endfaces, however, and much effort is expended in polishing severed fiber ends to tolerances of less than one degree from perpendicularity. An improvement in the preparation process was realized in the perpendicular fracturing of the fiber as described by Gloge et al. in U.S. Pat. No. 4,027,814. Utilizing the natural tendency of fibers to fracture in a perpendicular plane, Gloge et al. developed their method of controlling bending stress to ensure that such a fractured endface was devoid of light-scattering sites. Other tools, such as the Model CT-07 marketed by Alcoa Fujikura Ltd., Spartansburg, S.C., have been devised to obtain perpendicular endface fractures in optical fibers.
A number of studies, for example, Young et al., "Optimization of Return Loss and Insertion Loss Performance of Single-Mode Fiber Mechanical Splices", IWCS Conference, Reno, Nev. (1988), have indicated that improved return loss can be obtained in mechanical optical fiber splices through the use of fiber endfaces that deviate from the perpendicular by an angle in the range of about nine degrees. To implement this improvement the common practice of grinding and polishing the fiber endface was employed in forming the desired oblique angle. It was observed, however, that the polishing process causes a compaction of fiber material in the vicinity of the endface with a resulting localized variation in refractive index that introduces reflective sites adversely affecting splice return loss.
We have now discovered a method of obliquely fracturing optical fibers, typically having the standard 125 micrometer cladding diameter, in order to take advantage of the desirable effect of the resulting fiber endfaces on mechanical splice return loss while enjoying the additional physical and economical benefits of a fracturing process.